1. Field of the Invention
The present invention relates to a laminate film having good winding suitability and high uniformity of optical properties and to an optically compensatory film, a polarizing plate, and a liquid crystal display device each having the same.
2. Background Art
Patent Document 1 discloses a cellulose acylate laminate film in which an outer layer containing a prescribed cellulose acylate and an inner layer containing a prescribed cellulose acylate are laminated. A laminate film in which an outer layer is laminated on an inner layer, as disclosed in JP-A-2010-58331, is useful for various optical films, for example, various optical films used for liquid crystal display device, in view of the fact that optical properties which cannot be achieved by only an inner layer can be achieved.
Now, in general, a longitudinal film to be continuously manufactured is wound up in a roll form for the purpose of storage, conveyance, etc. But, when a film having a uniform film thickness is wound up in a roll form, there may be the case where fine scratches are produced on the surface of the film due to tightness of winding. When used for various applications, there may be the case where such a scratch becomes a fault to cause a reduction of the performance. For example, though an optically compensatory film formed of a support film having thereon an optically anisotropic layer having alignment of a liquid crystal composition immobilized thereto has hitherto been used for liquid crystal display devices, there may be the case where if a film having a fine scratch on the surface thereof is used as the support film of the optically compensatory film, the alignment of the liquid crystal composition to be coated on the surface is affected, and the scratch portion becomes a luminescent spot, thereby reducing the display performance of the liquid crystal display device.
Then, as for the continuously produced film, in order to suppress the tightness of winding, in general, it is performed to make the thickness of the both end parts thicker than that in the central part in the width direction. But, in the foregoing laminate film in which an outer layer is laminated on an inner layer, in general, the inner layer and the outer layer are different from each other with respect to a formulation of the raw material composition. Since the difference in a formulation of the raw material composition affects optical properties of the film, a difference of the thickness in the film width direction brings ununiformity of the optical properties in the film width direction. Since in the both end parts, the thickness is thick, a concentration of additives is high. The higher the concentration of additives, the lower the elastic modulus is. Therefore, for example, when a stretching treatment is applied for the purpose of revealing optical properties, the end parts tend to be more stretched, and the ununiformity of optical properties in the width direction becomes larger depending upon a difference in degree of stretching.